Multicolor electrophotographic printing device with bipolar toner

Abstract

A multicolor printer uses toner of two polarities applied on a photo conductor layer prior to the two toners being applied to a carrier. The photo conductor layer is provided with an image-wise illumination with regions of different illumination to form regions of different potentials. The regions of different potentials are developed by applying the toner of two polarities. Further colors of toner may be used, provided illumination with corresponding different illumination and provided charging of the photo conductor layer to change relative potentials is performed. An overall illumination of the photo conductor layer between developing steps changes potential levels on regions not covered by toner but not in areas covered by toner.

What is claimed is:  
     
       1. A method for electrophotographic printing of a print image with a plurality of colors on a carrier, comprising the steps of: 
       charging a layer system to a starting potential,  
       generating at least three different potentials on the layer system by image-wise illuminating, one potential of said three potentials having a value that is greater in terms of amount than another potential of said at least three different potentials and a first potential of said at least three different potentials having a value that is greater in terms of amount than said one potential,  
       in a developing step with first color particles of a first color and first polarity, applying said first color particles onto locations having said first potential,  
       in a developing step with second color particles of a second color and of a second polarity, applying said second color particles onto locations having said another potential,  
       increasing potential on locations already covered with color particles in terms of amount at least once,  
       lowering said one potential in terms of amount by uniform illuminating to a value below a momentary value of said another potential that is present after said developing step with said second color particles of the said second color, and,  
       in a developing step with third color particles of a third color of the second polarity, applying said third color particles at locations having the lowered one potential.  
     
     
       2. A method according to claim  1 , wherein said layer system includes a photo conductor layer and an electrode layer carrying a predetermined reference potential and comprising the steps of: 
       providing the print image with  
       at least one first image element of said first color,  
       at least one second image element having a color of the carrier,  
       at least one third image element having said third color, and  
       at least one fourth image element having said second color,  
       allocating a first surface element of said photo conductor layer to the at least one first image element,  
       allocating a second surface element of said photo conductor layer to the at least one second image element,  
       allocating a third surface element of said photo conductor layer to the at least one third image element, and  
       allocating a fourth surface element of the photo conductor layer to the at least one fourth image element,  
       wherein said charging step includes charging the first and second and third and fourth surface elements to a negative starting potential;  
       wherein said generating step includes differently illuminating the first and second and third and fourth surface elements such that said first surface element has said first potential, said second surface element has a second potential, said third surface element has a third potential and the fourth surface element has a fourth potential being said another potential and the third potential being said one potential that is higher in amount compared to the fourth potential and the second potential being higher in amount compared to the third potential and the first potential being higher in terms of amount compared to the second potential following illumination;  
       wherein in said developing step with said first color particles the surface elements are developed with said first color particles of the first color, including depositing positively charged first color particles of the first color on the first surface element upon employment of a first auxiliary electrode that has a first auxiliary potential that is higher in terms of amount than a momentary potential on the second surface element and lower in terms of amount than a momentary potential on the first surface element;  
       wherein in said developing step with said second color particles the surface elements are developed with second color particles of the second color, including depositing negatively charged second color particles of the second color on the fourth surface element upon employment of a second auxiliary electrode that has a second auxiliary potential that is higher in terms of amount than a momentary potential on the fourth surface element and lower in terms of amount than a momentary potential on the third surface element;  
       wherein said step of increasing potential includes arranging the surface elements close to a light source having an approximately uniform light distribution so that the first surface element covered with said first color particles and the fourth surface element covered with said second color particles are illuminated substantially less than the second surface element and the third surface element which are not covered with color particles, said illuminating being for a duration sufficient to cause a momentary potential on the third surface element to be reduced in terms of amount to a potential that is lower in terms of amount than a momentary potential on the fourth surface element; and  
       wherein in said developing step with third color particles the surface elements are developed with third color particles of the third color, including depositing negatively charged third color particles of the third color on the third surface element upon employment of a third auxiliary electrode that has a third auxiliary potential that is higher in terms of amount than a momentary potential on the third surface element and lower in terms of amount than a momentary potential on the fourth surface element and a momentary potential on the second surface element.  
     
     
       3. A method according to claim  1 , wherein said layer system includes a photo conductor layer and an electrode layer carrying a predetermined reference potential and comprising the steps of: 
       providing the print image with  
       at least one first image element of said first color,  
       at least one additional image element of said third color and  
       at least one another image element of said second color,  
       allocating a first surface element of said photo conductor layer to the at least one first image element,  
       allocating an additional surface element of said photo conductor layer to the additional image element and  
       allocating another surface element of the photo conductor layer to the another image element,  
       wherein said charging step includes charging the first surface element and said additional surface element and said another surface element to a negative starting potential,  
       wherein said generating step includes differently illuminating the first surface element and said additional surface element and said another surface element such that the another surface element has said another potential and the additional surface element has an additional potential that is higher in terms of amount compared to the another potential and the first surface element has said first potential that is higher in terms of amount compared to the additional potential,  
       wherein in said developing step with said first color particles the surface elements are developed with said first color particles of the first color, including depositing positively charged first color particles of the first color on the first surface element upon employment of a first auxiliary electrode that has a first auxiliary potential that is higher in terms of amount than a momentary potential on the additional surface element and lower in terms of amount than a momentary potential on the first surface element,  
       wherein in said developing step with said second color particles the surface elements are developed with said second color particles of the second color, including depositing negatively charged second color particles of the second color on the another surface element upon employment of a second auxiliary electrode that has a second auxiliary potential that is higher in terms of amount than a momentary potential on the another surface element and lower in terms of amount than a momentary potential on the additional surface element,  
       wherein said step of increasing potential includes arranging the surface elements close to a light source having an approximately uniform light distribution so that the first surface element covered with said first color particles and the another surface element covered with said second color particles are illuminated substantially less than the additional surface element which is not covered with color particles, said arranging being for a duration sufficient to cause a momentary potential on the additional surface element to be reduced in terms of amount to a potential that is lower in terms of amount than a momentary potential on the another surface element,  
       wherein in said developing step with said third color particles the surface elements are developed with said third color particles of the third color, including depositing negatively charged third color particles of the third color on the additional surface element upon employment of a third auxiliary electrode that has a third auxiliary potential that is higher in terms of amount than a momentary potential on the additional surface element and lower in terms of amount than a momentary potential on the another surface element.  
     
     
       4. A method according to claim  3 , wherein the print image contains at least one further picture element of a further color, comprising the steps of: 
       allocating the further picture element to a further surface element of the photo conductor layer,  
       charging the further surface element to the starting potential,  
       illuminating the further surface element such that said further surface element has a further potential that is higher in terms of amount than the additional potential and lower in terms of amount than the first potential following the illumination,  
       repeatedly arranging the surface elements close to an additional light source so that said further surface element which is not covered with color particles is considerably more illuminated than surface elements covered with color particles, said arranging step causing the potential on the further surface element to be reduced in terms of amount, and  
       developing the surface elements with color particles of the further color, including depositing negatively charged color particles of the further color on the further surface element upon employment of a further auxiliary electrode that has a further auxiliary potential that is higher in terms of amount than a momentary potential on the further surface element and lower in terms of amount than a momentary potentials on the other surface elements.  
     
     
       5. A method according to claim  1 , further comprising the step of: 
       recharging deposited color particles having a positive polarity to a negative polarity.  
     
     
       6. A method according to claim  1 , wherein said layer system includes a photo conductor layer and an electrode layer carrying a predetermined reference potential and comprising the steps of: 
       providing the print image with  
       at least one first image element of said first color,  
       at least one second image element having a color of the carrier,  
       at least one third image element having said third color, and  
       at least one fourth image element having said second color,  
       allocating a first surface element of said photo conductor layer to the at least one first image element,  
       allocating a second surface element of said photo conductor layer to the at least one second image element,  
       allocating a third surface element of said photo conductor layer to the at least one third image element, and  
       allocating a fourth surface element of the photo conductor layer to the at least one fourth image element,  
       wherein said charging step includes charging the first surface element and said second surface element and said third surface element and said fourth surface element to a positive starting potential,  
       wherein said generating step includes differently illuminating the surface elements such that the third surface element has said one potential and the second surface element has a second potential higher in amount compared to the one potential and the first surface element has said first potential that is higher in terms of amount compared to the second potential following illumination,  
       wherein in said step of developing with the third color particles the surface elements are developed with third color particles of the third color, including depositing positively charged third color particles of the third color on the third surface element upon employment of a first auxiliary electrode that has a first auxiliary potential that is higher in terms of amount than a momentary potential on the third surface element and lower in terms of amount than a momentary potential on the second surface element,  
       wherein said step of increasing potential includes arranging the surface elements close to a light source having an approximately uniform light distribution so that the third surface element covered with third color particles is illuminated substantially less than the first surface element and the second surface element which are not covered, said arranging for a duration sufficient to cause a momentary potential on the second surface element to be reduced in terms of amount to a potential that is lower in terms of amount than a momentary potential on the third surface element,  
       developing the surface elements with color particles of the second color, including depositing positively charged second color particles of the second color on the fourth surface element upon employment of a second auxiliary electrode that has a second auxiliary potential that is higher in terms of amount than a momentary potential on the fourth surface element and lower in terms of amount than a momentary potential on the third surface element and a momentary potential on the first surface element.  
     
     
       7. A method according to claim  1 , wherein said layer system includes a photo conductor layer and an electrode layer carrying a predetermined reference potential and comprising the steps of: 
       providing the print image with  
       at least one first image element of said first color,  
       at least one additional image element having said third color, and  
       at least one another image element having said second color,  
       allocating a first surface element of the photo conductor layer to the first image element,  
       allocating an additional surface element of the photo conductor layer to the additional image element, and  
       allocating another surface element of the photo conductor layer is allocated to the another image element,  
       wherein said charging step includes charging the surface elements to a positive starting potential;  
       wherein said generating step includes differently illuminating the surface elements such that the another surface element has said another potential and the additional surface element has an additional potential higher in amount compared to the another potential, and the first surface element has said first potential that is higher in terms of amount compared to the additional potential;  
       wherein in said developing step with the first color particles the surface elements are developed with first color particles of the first color, including depositing negatively charged first color particles of the first color on the first surface element upon employment of a first auxiliary electrode that has a first auxiliary potential that is higher in terms of amount than a momentary potential on the additional surface element and lower in terms of amount than a momentary potential on the first surface element;  
       wherein in said developing step with the second color particles the surface elements are developed with second color particles of the second color, including depositing positively charged second color particles of the second color on the another surface element upon employment of a second auxiliary electrode that has a second auxiliary potential that is higher in terms of amount than a momentary potential on the another surface element and lower in terms of amount than a momentary potential on the additional surface element;  
       wherein said step of increasing potential includes positioning the surface elements close to a light source having an approximately uniform light distribution so that the first surface element covered with first color particles and the another surface element covered with second color particles are illuminated substantially less than the additional surface element which is not covered, said positioning the surface elements close to a light source causing a momentary potential on the additional surface element to be reduced in terms of amount to a potential that is lower in terms of amount than a momentary potential on the another surface element;  
       wherein in said step of developing with said third color particles the surface elements are developed with third color particles of the third color so that positively charged third color particles of the third color are deposited on the additional surface element upon employment of a third auxiliary electrode that has a third auxiliary potential that is higher in terms of amount than a momentary potential on the additional surface element and lower in terms of amount than a momentary potential on the another surface element.  
     
     
       8. A method according to claim  6 , further comprising the steps: 
       providing the print image with at least one further image element of a further color,  
       allocating the further image element to a further surface element of the photo conductor layer,  
       charging the further surface element to the positive starting potential,  
       illuminating the further surface element such that said further surface element has a further potential that is higher in terms of amount than the one potential and lower in terms of amount than the second potential,  
       repeatedly arranging the surface elements close to an additional light source so that the further surface element which is not covered is respectively illuminated considerably more than the surface elements covered with color particles causing the potential on the further surface element to be reduced in terms of amount, and  
       developing the surface elements with color particles of the further color, including depositing positively charged color particles of the further color on the further surface element upon employment of a further auxiliary electrode that has a further auxiliary potential that is higher in terms of amount than a momentary potential on the further surface element and lower in terms of amount than a momentary potentials on the other surface elements.  
     
     
       9. A method according to claim  6 , further comprising the steps of: 
       wherein in said developing step with said first color particles, the surface elements are developed with said first color particles of the first color, including depositing negatively charged first color particles of the first color on the first surface element upon employment of an additional auxiliary electrode that has an additional auxiliary potential that is higher in terms of amount that a momentary potential on the second surface element and lower in terms of amount than a momentary potential on the first surface element;  
       recharging said negatively charged first color particles which have been deposited onto the photo conductor layer in said developing step with said first color particles to a positive polarity.  
     
     
       10. A method according to claim  1 , further comprising the step of: 
       transferring said first and second and third color particles which have been deposited onto a photo conductor layer in said developing steps onto the carrier from the photo conductor layer while substantially retaining their mutual positions.  
     
     
       11. A method according to claim  1 , further comprising the step of: 
       transferring deposited color particles onto an intermediate carrier while substantially retaining their mutual positions, and  
       transferring the color particles from the intermediate carrier onto the carrier while substantially retaining their mutual positions.  
     
     
       12. An electrophotographic printer, comprising: 
       a light-sensitive layer system that contains an electrode layer carrying a predetermined reference potential and a photo conductor layer,  
       a charging means for generating a starting potential on the photo conductor layer,  
       an illumination means for image-wise illumination of the photo conductor layer,  
       a first developer station for applying color particles of a first polarity and a first color onto the light-sensitive layer system,  
       a second developer station for depositing color particles of a second polarity and a second color onto the layer system,  
       at least one total illumination unit for uniform illumination,  
       at least one further developer station for applying color particles of the second polarity and a further color onto the layer system, and  
       at least one potential-increasing means for increasing a respective lowest potential on the layer system in terms of amount.  
     
     
       13. An electrophotographic printer according to claim  12 , further comprising: 
       a recharging station for charging the applied color particles of the first polarity to the second polarity.  
     
     
       14. An electrophotographic printer according to claim  12 , further comprising: 
       a transfer means for transferring the applied color particles from the layer system onto a carrier.  
     
     
       15. An electrophotographic printer according to claim  12 , further comprising: 
       an erase means for erasing a residual charge image on the layer system.  
     
     
       16. An electrophotographic printer according to claim  12 , further comprising: 
       a cleaning means for cleaning the layer system.  
     
     
       17. An electrophotographic printer, comprising: 
       a light-sensitive layer system that contains an electrode layer carrying a predetermined reference potential and a photo conductor layer;  
       a charging station for generating a starting potential on the photo conductor layer;  
       a character generator for image-wise illumination of the photo conductor layer;  
       a first developer station for applying color particles of a first polarity and a first color onto the light-sensitive layer system;  
       a second developer station for depositing color particles of a second polarity and a second color onto the layer system;  
       at least one illumination unit for uniform illumination;  
       at least one further developer station for applying color particles of the second polarity and a further color onto the layer system; and  
       at least one potential-increasing station for increasing a respective lowest potential on the layer system in terms of amount.